The present invention relates generally to metal casting methods, and more particularly to a method for efficiently producing a metal casting mold for a complex part by recursively identifying the cores for the casting and the molds for making the cores defining the complex part once a parting surface for the part is defined.
In metal casting discrete mechanical parts using sand molds, patterns are used in fabrication of the molds to ensure that the resulting cast parts have the correct geometry, or can be readily finished to the correct geometry. The pattern is a model of a part to form a mold cavity substantially defining the part shape, but is not simply a facsimile of the part because additional shapes (sprues, runners, gates, etc) are used to form channels for inserting molten metal, or shape modifications to provide taper (draft) on some surfaces of the part to facilitate withdrawal of the part from the mold. The principal molding material conventionally used in foundries is silica sand, which, when mixed with water and a binder (e.g. clay), can be formed to a complex geometry which retains its shape while being filled with metal and allowed to cool. The mold is usually destroyed when the casting is removed and must be recreated using the pattern for each cast part to be produced.
Mold design and fabrication are especially difficult if the cast part has sufficiently complex geometry or when the parting surface is defined such that the pattern cannot be withdrawn easily from the mold. In order to accommodate complex geometries by means of conventional casting methods, the pattern maker uses cores and loose pieces to ensure that those parts of the cavity which should be filled are filled. In standard practice, molds are often made up of two halves. The pattern is also made up of two parts mounted on the two sides of a board which represents the dividing (parting) surface (which may be more complex than a single plane) between the two mold halves. The two mold halves are formed by packing sand around each side of the pattern board, and subsequently combined to form the cavity left when the pattern is removed. The mold must therefore be made such that the pattern can be withdrawn from the mold. If the mold is made in two halves, each part of the pattern must be removable from the corresponding mold half. In order to define the casting pattern, the pattern maker modifies the pattern around the complex features of the part (to render it removable from the mold) using extra pieces of mold-like material, called cores or loose pieces, for filling extraneous spaces around the correct cavity shape for the cast part. The cores are generally made from bonded silica sand, and the molds used to make the cores, called core boxes, are permanent molds, usually made of wood or hardened epoxy.
In the practice of the invention, computer associative memories and feature-based computer aided design (CAD) are incorporated into a highly efficient and effective method for producing patterns and molds for casting substantially any complex part wherein withdrawal interferences of the pattern are defined for various parting planes or surfaces, and, once the parting surface is specified, the correct pattern structure is recursively defined.
It is a principal object of the invention to automate and optimize foundry tooling fabrication for metal casting.
It is another object of the invention to provide a method for producing a pattern for a part to be cast in a metal casting process.
It is another object of the invention to provide a method for sequentially drafting a pattern by part feature, core and rigging relative to a parting plane of a casting mold.
It is another object of the invention to provide a method for producing casting patterns for complex cast parts which cannot be otherwise withdrawn from a mold without destroying the mold.
It is a yet further object of the invention to provide a solid modelling recursive molding procedure for defining casting pattern core and core box requirements.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.